Method of treating a carbon current collection brush blank and brush resulting therefrom

ABSTRACT

A method of treating a carbon current collection brush blank for increased high temperature and low humidity life in a brush comprises contacting the brush blank with a solution of zinc naphthenate and baking the brush at a temperature from 180*C to 200*C thereby reducing the amount of zinc naphthenate to 4 to 6 weight percent of the brush blank weight. A carbon current collection brush has a carbon body which body contains from 4 to 6 weight percent of zinc naphthenate.

United States Patent Grunewald et al.

14 1 Oct. 15, 1974 METHOD OF TREATING A CARBON CURRENT COLLECTION BRUS/l-I BLANK AND BRUSH RESULTING TI-IEREFROM Inventors: Albert L. Grunewald, Stroudsburg,

Pa.; George II. Gunnoe, Schenectady, NY.

Assignee: General Electric Company, Lynn,

Mass.

Filed: Sept. 14, 1972 Appl. No.: 289,173

US. Cl 117/228, 117/119, 252/510, 264/29, 264/105, 310/228, 310/249,

Int. Cl B44d 1/20, B44d 1/46 Field of Search 117/228, 119; 282/510; 264/29, 108; 310/228, 249, 252, 253

adi.

BRUSH LIFE -1900RS' E i 1 1 [56] References Cited UNITED STATES PATENTS 2,881,100 4/1959 Hardmun 117/228 3,751,294 8/1973 Fridman et al. 117/228 x Primary Examiner-Mayer Weinblatt 5 7 ABSTRACT 9 Claims, 2 Drawing Figures 1 l l l l I l I 1 1 Mo //0 d0 no #10 1'50 Asa 1&0 $0 1110 2'00 RUSH TEMPERATURE METHOD OF TREATING A CARBON CURRENT COLLECTION BRUSH BLANK AND BRUSH RESULTING THEREFROM This invention relates to methods of treating carbon current collection brush blanks, and to brushes resulting therefrom and, more particularly, to such methods to produce brush blanks for operation in brushes at elevated temperatures.

Carbon current collection brushes are employed in rotating brush-type machines in which the brush blanks are generally fabricated of carbon, a relatively poor electrical conductor, reinforced by other materials and graphitized. Graphite is also employed for such brush blanks. For example, carbon is mixed with a pitch binder and the mixture is graphitized.

The blanks are then assembled into brushes. These brushes are referred to as carbon current collection brushes or merely as carbon brushes.

The above types of carbon brushes are retained in position by brush holders which generally are in the form of square, rectangular or cylindrical sleeves serving as a guide for any radial motion of the brush resulting from vibration or eccentricity of the armature. The brush holder may be mounted on a bracket to maintain a rigid position spaced from the commutator surface. An adjustable spring connected to the bracket bears on the top surface of the brush to maintain a desired contact pressure of the bottom surface of the brush upon the commutator segments or slip ring.

With such carbon current collection brushes or carbon brushes, as these brushes are generally referred to, the wear rate of the brush in electric motors, for example, increases very rapidly with increasing ambient temperature. The life of a typical carbon brush under a standard load of 100 amperes per square inch for 250 mils brush wear decreases from about 8,500 hours at 100C to about 700 hours at 200C. An important contributing factor to increased wear at elevated temperatures is direct oxidation of the carbon brush surface at the sliding interface, leading to loss of carbon as gaseous oxides. This oxidation is catalyzed by the presence of the copper in the commutator or slip ring. Minute particles of copper oxide migrate along the basal planes of the graphite crystallites into the interior of the brush producing a catalytic effect which leads to enhanced gasification rates and to increased brush porosity. Various approaches have been employed in attempts to overcome such rapid brush wear including use of lubricants.

The present invention is directed to an improved method of treating a conventional carbon current collection brush blank and to an improved carbon brush resulting therefrom which is useful at elevated temperatures and low humidity of -60 dewpoint.

The primary objects of our invention are to provide a method of treating a carbon brush blank in which the.

brush exhibits characteristics of operability at elevated temperatures and low humidity with reduced wear rate.

The above objects and other objects, features and advantages of the invention will be better understood from the following description taken in connection with the accompanying drawing in which:

FIG. 1 is a side elevational view, partly in section, of a carbon brush, made in accordance with our invention, in a brush holder assembly; and

FIG. 2 is a graph plotting carbon brush temperature in degrees centigrade against carbon brush wear in hours per 250 mils of wear.

in FIG. 1 of the drawing there is shown a single brush holder assembly 10 including an improved carbon current collection brush 11 made in accordance with our invention. Carbon brush 11 comprises a body portion 12 and a lower surface portion 13, which surface is in contact with or rides on the surface of a commutator 14 or a slip ring due to the force of a spring applied by brush spring 15 against the top of body portion 12 of carbon brush 10. Carbon brush 10 is maintained in its desired position relative to commutator 14 or to a slip ring by means of brush holder 16 which is held in a fixed position spaced from the surface of commutator 14 by means of bracket 17. Brush holder 16 is shown of conventional design comprising a rectangular sleeve fabricated of a high strength metal and serves as a guide for any radial motion of carbon brush 11 resulting from vibration or eccentricity of the armature or commutator. For purposes of simplicity, the flexible copper cable generally described as a brush shunt or pigtail which is often employed for directing the current from the carbon brush to the brush holder is not illustrated but can be employed, as desired. Carbon brush 11 or at least its surface 13 contains from 4.0 to 6.0 weight of zinc naphthenate.

We found that a carbon current collection or carbon brush which contained from 4.0 to 6.0 weight percent of zinc naphthenate therein or at least in a surface portion had an increased operating factor of about 7.7 versus a conventional carbon collection or carbon brush at amperes/square inch at an elevated temperature of 200C. We found further that our carbon brush had also an increased operating factor of about 1.1 at 100C.

In FIG. '2 there is shown a graph plotting carbon brush temperature against brush wear. Curves I and 11 show graphically the results of standard wear tests under load. Each such test involves applying a standard current rating of 100 amperes per square inch and a sliding velocity of 2,500 feet per minute. Each test is to determine thenumber of hours of brush life until 250 mils of the brush surface is worn away.

Curve 1 shows the results of the above testing of a conventional carbon collection brush while curve 11 shows the results of the above testing of a brush made in accordance with our invention. The test temperatures are set forth in degrees centigrade while the brush life is set forth in hours, which hours represent 250 mils of brush wear. As it is seen, the brush made in accordance with our invention is superior at elevated temperatures and a definite improvement at a conventional temperature of 100C.

We found that our method of treating a carbon current collection brush blank with a solution of zinc naphthenate inhibited the catalytic effect of the copper oxide which had migrated into the brush from the commutator or slip ring during brush operation. This treatment reduced the normally resulting enhanced gasification rates and increased brush porosity. Our improved carbon brush exhibited substantially longer life at elevated temperatures.

We found that we could form an improved carbon current collection brush by treating a conventional carbon brush blank in the following unique manner. A conventional carbon brush blank is contacted with a solution of zinc naphthenate, whose empirical formula corresponds to Zn O (OOCR) where RCOO'represents the naphthenate radical. Zinc naphthenate solution is commercially available. The blank is contacted with the zinc naphthenate preferably by vacuum impregnating a solution of zinc naphthenate and mineral spirits into the brush blank.

In our preferred method, we air dry the impregnated brush blank for a period of 16 hours. The brush blank is then baked preferably by raising its temperature to 200C in a period of 16 hours. In this preferred method the amount of zinc naphthenate in the brush blank is reduced to 4 to 6 weight percent of the brush blank weight. After the brush blank is treated in this manner, the brush blank is formed in a conventional manner into a carbon current collection brush.

We found that by employing our above method we provide an improved carbon current collection brush comprising a carbon body containing from 4 to 6 weight percent of zinc naphthenate. While it should be appreciated that various other concentrations of zinc naphthenate in a solution may be employed, we found the preferable solution to be 8 percent zinc naphthenate in mineral spirits. The blank may be wholly or partially immersed in such a solution sothat the entire blank or at least the contact surface is impregnated with the zinc naphthenate solution. Further, the brush blank is baked at a temperature in a temperature range from 180 to 200C thereby reducing the amount of zinc naphthenate in the brush blank to 4 to 6 percent of the brush blank weight. Higher concentrations of zinc naphthenate which result from no baking or insufficient baking result in a brush with subsequent high friction on the brush commutator or slip ring interface.

We employed also an 8 weight percent solution of cadmium naphthenate in mineral spirits. A brush blank was vacuum impregnated in this solution, air dried and subsequently baked as described above for the zinc naphthenate treatment. The brush, which was formed from this blank, failed to provide the improvement in performance of our brush which contained from 4.0 to 6.0 weight percent of zinc naphthenate.

We found that in accordance with our method we provided a substantial brush improvement when under load at 200C. Additionally, we found that our brush performed in a very satisfactory manner under low humidity conditions. Normally, the combination of low humidity conditions and high temperature result in ex cessive brush wear.

Carbon current collection brushes made in accordance with the method of our invention are set forth below:

EXAMPLE I A conventional carbon current collection brush blank of graphitized carbon was contacted with an 8 percent zinc naphthenate in mineral spirits solution by being vacuum impregnated. The blank was air dried for 16 hours. The brush was then baked by being heated to 200C in 16 hours. The resulting blank contained between 4 and 6 percent zinc naphthenate. The blank was formed conventionally into a brush.

EXAMPLE ll Two standard wear tests under load were performed on the brush of Example I. The first wear test was performed at C while the second wear test was performed at an elevated temperature of 200C. Each test involved a standard current rating of 100 amperes per square inch and a sliding velocity of 2,500 feet per minute. The brush was mounted in a brush holder and employed in the fashion shown generally in the single FIG- URE of the drawing. ln theExample and subsequent Examples,- the standard wear test is to determine the number of hours of brush life until 250 mils of the brush surface is worn away. Thus, the results of each test are set forth in hours which is the life of the particular brush. At 100C the brush exhibited 10,400 hours. At 200C the brush exhibited 5,400 hours.

EXAMPLE Ill For comparison purposes with our improved brush of Examples I and II, a conventional carbon current collection brush of graphitized carbon which was not treated in accordance with our method exhibited 8,500 hours of brush life at 100C. However, at 200C this conventional carbon brush exhibited only 700 hours of life. Thus, it .will be seen that at an elevated temperature of 200C that the carbon brush treated in accordance with our method exhibits almost a 7.7 fold improvement over the conventional carbon brush. v

EXAMPLE IV Two wear tests under load at low humidity were performed on a brush made as described above in Example l. The first wear test was performed at 100C while the second wear test was performed at an elevated temperature of 200C. Each test involved a standard current rating of 100 amperes per square inch and a sliding velocity of 2,500 feet per minute. Each test was conducted at a low humidity of -50F dewpoint. The brush was mounted in a brush holder and employed in the fashion shown generally in the single FIGURE of the drawing. As described above in Example II, the wear test is to determine the number of hours of brush life until 250 mils of the brush surface is worn away. Thus, the results of each test are set forth in hours which is the life of the particular brush. At 100C the brush exhibited 2,000 hours. At 200C the brush exhibited 3,049 hours.

While other modifications of the invention and variations thereof which may be employed within the scope of the invention have not been described, the invention is intended to include such as may be embraced within the following claims:

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A method of treating a carbon current collection brush blank which comprises providing a carbon current collection brush blank, contacting the brush blank with a solution of zinc naphthenate, baking the brush blank at a temperature in the temperature range of from 180 to 200C thereby reducing the amount of zinc naphthenate in the brush blank to 4 to 6 weight percent of the brush blank weight.

2. A method of treating a carbon current collection brush blank as in claim 1, in which the brush blank is vacuum impregnated with a solution of zinc naphthenate.

3. A method of treating a carbon current collection brush blank as in claim 1, in which the solution is 8 percent zinc naphthenate in mineral spirits.

4. A method of treating a carbon current collection period of 16 hours, baking the brush blank by raising brush blank as in claim 1, in which the brush is air dried its temperature to 200 in 16 hours thereby reducing for a period of 16 hours prior to baking. the amount of zinc naphthenate in the brush blank to 5. A method of treating a carbon current collection 4 to 6 weight percent of the brush blank weight. brush blank as in claim 4, in which the brush blank is 5 7. A method of forming a carbon current collection baked by raising the temperature to 200C in 16 hours. brush as in claim 6, wherein the brush blank is formed into a brush.

6. A method of treating a carbon current collection 8. A carbon current collection brush produced by the brush blank which comprises providing a carbon curmethod of claim 1. rent collection brush blank, vacuum impregnating a so- 9. A carbon current collection brush produced by the lution of 8 percent zinc naphthenate in mineral spirits method of claim 6. into the brush blank, air drying the brush blank for a 

1. A METHOD OF TREATING A CARBON CURRENT COLLECTION BRUSH BLANK WHICH COMPRISES PROVIDING A CARBON CURRENT COLLECTION BRUSH BLANK, CONTACTING THE BRUSH BLANK WITH A SOLUTION OF ZINC NAPHTHENATE,, BAKING THE BRUSH BLANK AT A TEMPERATURE IN THE TEMPERATURE RANGE OF FROM 180* TO 200*C THEREBY REDUCING THE
 2. A method of treating a carbon current collection brush blank as in claim 1, in which the brush blank is vacuum impregnated with a solution of zinc naphthenate.
 3. A method of treating a carbon current collection brush blank as in claim 1, in which the solution is 8 percent zinc naphthenate in mineral spirits.
 4. A method of treating a carbon current collection brush blank as in claim 1, in which the brush is air dried for a period of 16 hours prior to baking.
 5. A method of treating a carbon current collection brush blank as in claim 4, in which the brush blank is baked by raising the temperature to 200*C in 16 hours.
 6. A method of treating a carbon current collection brush blank which comprises providing a carbon current collection brush blank, vacuum impregnating a solution of 8 percent zinc naphthenate in mineral spirits into the brush blank, air drying the brush blank for a period of 16 hours, baking the brush blank by raising its temperature to 200* in 16 hours thereby reducing the amount of zinc naphthenate in the brush blank to 4 to 6 weight percent of the brush blank weight.
 7. A method of forming a carbon current collection brush as in claim 6, wherein the brush blank is formed into a brush.
 8. A carbon current collection brush produced by the method of claim
 1. 9. A carbon current collection brush produced by the method of claim
 6. 